CPCE Fluid Flow & Heat Transfer Analysis 4

Question 1

In CFD, what is the primary purpose of the wall y+ value in turbulent boundary layer modeling?

Accepted Answer

To ensure appropriate mesh resolution for the chosen near-wall treatment

Answer

The dimensionless wall distance y+ determines whether the near-wall mesh is fine enough to resolve the viscous sublayer or whether wall functions should be used.

Question 2

What is the physical significance of the thermal entry length in duct flow?

Accepted Answer

The duct length over which the thermal boundary layer grows to fill the duct

Answer

The thermal entry length is the downstream distance from the inlet where the thermal boundary layer fully develops and heat transfer transitions to the fully-developed profile.

Question 3

Which CFD boundary condition is most appropriate for a fully-developed flow outlet in an internal flow simulation?

Accepted Answer

Zero-gradient (outflow) condition for all variables

Answer

A zero-gradient (outflow) condition assumes that flow variables do not change in the streamwise direction at the outlet, appropriate for fully-developed exit conditions.

Question 4

In the energy equation for CFD, what does the viscous dissipation term represent?

Accepted Answer

Conversion of kinetic energy to heat through viscous stresses

Answer

Viscous dissipation represents the irreversible conversion of mechanical energy to thermal energy due to viscous stresses within the fluid, becoming important at high velocities or in highly viscous flows.

Question 5

What is the key characteristic of a pressure-based CFD solver compared to a density-based solver?

Accepted Answer

Uses pressure as the primary variable for incompressible and low-speed flows

Answer

Pressure-based solvers use the pressure field as the primary variable and are well-suited for incompressible and mildly compressible flows where density variations are small.

(CPCE) Certified Professional CFD Engineer Practice Test

(CPCE) Certified Professional CFD Engineer Practice Test

CPCE Fluid Flow & Heat Transfer Analysis 4